Tyre for vehicle wheels with a reinforced bead

ABSTRACT

Tyre for vehicle wheels comprising; a) a carcass structure having at least one carcass ply associated with respective left and right bead wires, each bead wire being enclosed in a respective bead, said bead comprising a bead filler b) a belt structure comprising at least one belt strip applied circumferentially over said carcass structure; c) a tread band circumferentially superimposed on said belt structure; d) a pair of side walls applied laterally on opposite sides relative to said carcass structure; in which said bead filter is obtained by vulcanization of an elastomeric composition comprising discontinuous fibres and at least one elastomeric groups. The abovementioned bead filler is capable of having a positive influence on the performance qualities of the tyre, in particular on the performance qualifies at high speed, such as, for example, the cornering stability, the control on a wet surface and the ride comfort.

The present invention relates to a tyre for vehicle wheels.

More particularly, the present invention relates to a tyre for vehiclewheels which has a reinforced bead, said bead comprising a bead fillerconsisting of a vulcanized elastomeric composition comprisingdiscontinuous fibres and at least one elastomeric polymer containingepoxide groups.

In general, a tyre comprises a carcass structure formed by at least onecarcass ply shaped in a substantially toroidal configuration, theopposite lateral edges of which are associated with substantiallyinextensible respective annular structures, commonly known as “beadwires”, a tread band, a belt structure located between the carcassstructure and the tread band, and a pair of sidewalls applied externallyto said carcass structure. The portion of the tyre which comprises theabovementioned bead wires is called the bead, and its function is to fixthe tyre onto a respective rim of a vehicle wheel. According to aconventional structure, the bead comprises a suitable rubber band, ofsubstantially triangular cross section, commonly known as “bead filler”.

U.S. Pat. No. 4,532,291 discloses a bead filler composition comprising:(A) a reinforced elastomeric composition comprising a vulcanizablerubber and from 5 to 100 parts by weight, per 100 parts by weight ofsaid vulcanizable rubber, of a thermoplastic polymer containing an amidegroup in the main chain (for example Nylon) in the form of short fibres,said vulcanizable rubber and said thermoplastic polymer being graftedtogether by means of a precondensed phenol-formaldehyde resin; (B) adiene rubber; and (C) carbon black. Examples of vulcanizable rubberswhich are useful for this purpose are: natural rubber,cis-1,4-polybutadiene, polyisoprene, styrene/butadiene copolymers,isoprene-isobutylene copolymers, and the like. Natural rubber ispreferred. Examples of diene rubbers (B) which are useful for thispurpose are: natural rubber, polyisoprene, cis-1,4-polybutadiene,styrene/butadiene copolymers, isoprene/isobutylene copolymers, and thelike, or blends thereof. Said composition is said to have a low Mooneyviscosity and good processibility and, after vulcanization, a highelastic modulus and high flex cracking propagation resistance.

U.S. Pat. No. 4,824,899 discloses a bead filler composition comprising(A) from 50 to about 100 parts by Weight of carbon black; (B) from 1 toabout 10 parts by weight of sulphur; and (C) from 1 to about 15 parts byweight of a metal salt of acrylic acid chosen from aluminium acrylate,zinc acrylate, nickel acrylate, cobalt acrylate, lead acrylate, ironacrylate, manganese acrylate, barium acrylate, calcium acrylate andmagnesium acrylate. Said parts by weight are defined as parts by weightrelative to 100 parts of natural rubber or of a blend of natural rubberwith not more than 50% of a synthetic diene rubber. Examples ofsynthetic diene rubbers which are useful for this purpose are:polyisoprene, cis-polybutadiene, polybutadiene with a middle or highcontent of vinyl, syndiotactic polybutadiene and styrene/butadienecopolymers in emulsion or in solution. Said composition is said to beusable as bead filler and to give the tyre good durability, good ridecomfort and good cornering stability.

U.S. Pat. No. 4,898,223 discloses a composition comprising apolyoctenamer, a cis-1,4-polyisoprene grafted with an alkyl methacrylateand at least one vulcanizable rubber chosen from natural rubber andsynthetic rubbers containing a carbon-carbon double bond. Saidcomposition is said to have good stiffness and to be usable as beadfiller.

Japanese patent application JP 07/330 962 discloses a bead fillercomposition comprising: (A) a polyolefin; (B) a vulcanizable rubber; and(C) fibres of a thermoplastic polymer containing an amide group in themain chain (for example Nylon). Said composition is said to have, aftervulcanization, a good elastic modulus and high flex cracking propagationresistance.

U.S. Pat. No. 4,871,004 discloses a composition comprising avulcanizable elastomer and an effective amount of aramid fibres.Examples of vulcanizable elastomers which are useful for this purposeare: natural rubber, cis-1,4-polyisoprene, polybutadiene (in solution orin emulsion), styrene/butadiene copolymers (in solution or in emulsion),butyl rubbers and halobutyl rubbers, EPDM, butadiene/acrylonitrilerubbers, neoprene, vinylpolybutadiene and, in general, polymers withviscoelastic properties, or blends thereof. Said composition is said tobe usable in all cases in which rubbers with a high level of hardnessand/or a high modulus are required, in particular in vehicle tyres (forexample as bead filler). One of the reasons which justifies the use ofthe abovementioned fibres is the improvement in the structural strengthof the vulcanized manufactured product.

The Applicant has found that the use of reinforcing fibres inelastomeric compositions does not always lead to the desired mechanicaland elastic properties being obtained. For example, elastomericcompositions comprising an elastomeric polymer, in particular naturalrubber, and discontinuous fibres, have mechanical properties, inparticular load at elongation, and elastic properties, in particulardynamic elastic modulus at high temperatures, that are unsatisfactory,in particular when said elastomeric compositions are used as beadfiller. In addition, the abovementioned compositions show a highpercentage of reversion which may lead to a decline in the properties ofthe final manufactured product, both in the case of an overvulcanizationin the production stage, and during the use of this manufacturedproduct. In particular, when they are used as bead filler, reversionphenomena may result in a deterioration of the road-holding of the tyre.Essentially, the reversion consists of a partial breaking and/orcyclization of the sulphur-based crosslinks between the polymer chainsof the elastomeric composition, which may be attributed substantially tothe high temperatures that are reached during the vulcanizationoperations and/or when the tyre is in use.

The Applicant has now found that it is possible to overcome thedrawbacks outlined above by using, as bead filler for a tyre, anelastomeric composition comprising discontinuous fibres and at least oneelastomeric polymer containing epoxide groups. Said composition, aftervulcanization, has mechanical properties, in particular load atelongation, and elastic properties, in particular dynamic elasticmodulus at high temperatures, that are such as to obtain a bead fillerwhich is capable of having a positive influence on the performancequalities of the tyre, in particular on the performance qualities athigh speed, such as, for example, the cornering stability, the controlon a wet surface and the ride comfort. In addition, said performancequalities are substantially maintained over time by means of asignificant reduction in the reversion phenomena.

According to a first aspect, the present invention thus relates to atyre for vehicle wheels comprising:

-   -   a carcass structure having at least one carcass ply shaped in a        substantially toroidal configuration, the opposite lateral edges        of which are associated with respective left and right bead        wires, each bead wire being enclosed in a respective bead, said        bead comprising a bead filler;    -   a belt structure comprising at least one belt strip applied        circumferentially over said carcass structure;    -   a tread band circumferentially superimposed on said belt        structure;    -   a pair of sidewalls applied laterally on opposite sides relative        to said carcass structure;        in which said bead filler is obtained by vulcanization of an        elastomeric composition comprising discontinuous fibres and at        least one elastomeric polymer containing epoxide groups.

According to a further aspect, the present invention relates to anelastomeric composition comprising discontinuous fibres and at least oneelastomeric polymer containing epoxide groups.

According to a further aspect, the present invention relates to avulcanized elastomeric manufactured product obtained by vulcanizing anelastomeric composition comprising discontinuous fibres and at least onepolymer containing epoxide groups.

According to one preferred embodiment, said elastomeric composition alsocomprises a diene elastomeric polymer not containing epoxide groups.

According to a further preferred embodiment, said elastomericcomposition also comprises at least one reinforcing filler.

According to a further preferred embodiment, said elastomericcomposition also comprises at least one thermosetting resin.

According to one preferred embodiment, the discontinuous fibres arearamid fibres, in particular short fibrillatedpoly(para-phenyleneterephthalamide) fibres (also known as aramid pulp),of the type known commercially as Kevlar® pulp from Du Pont or Twaron®pulp from Akzo, which are disclosed in U.S. Pat. No. 4,871,004 mentionedabove, the description of which is incorporated herein by way ofreference. Preferably, aramid fibres used according to the presentinvention have a configuration with a main trunk with a length (L) ofbetween about 0.2 mm and about 0.5 mm, a diameter (D) of between about0.005 mm and about 0.02 mm and an aspect ratio L/D of between about 10and about 1 000, and a plurality of fibrils or small branches whichextend outwards from said trunk over the entire length of the trunk andwhich have a diameter that is substantially smaller than the diameter ofsaid trunk. The surface area of said fibres is between about 4 m²/g andabout 20 m²/g. The surface area of the aramid fibres which may be usedin the present invention is from about 30 to about 60 times greater thanthat of fibres having the same diameter but not comprising fibrils.

According to a preferred embodiment, the abovementioned aramid fibresmay be used either as such or in the form of a predispersion in asuitable polymer matrix which serves as a vehicle, consisting of, forexample, natural rubber, butadiene/styrene copolymers, ethylene/vinylacetate copolymers, and the like. Preferably, a blend (“masterbatch”) inwhich the abovementioned fibres are dispersed in natural rubber, whichis known by the trade name Kevlare Engineered Elastomer from Du Pont andwhich is composed of 23% by weight of Kevlar® and 77% by weight ofnatural rubber, is used.

It should be pointed out that although the discontinuous fibres that arepreferred according to the present invention are chosen from the aramidfibres described above, said discontinuous fibres may also be chosenfrom: fibres based on other polyamides (for example Nylon), onpolyesters, on polyolefins, on polyvinyl alcohol, or glass fibres.

According to one preferred embodiment, the discontinuous fibres arepresent in the elastomeric composition in an amount of between 2 phr and12 phr, preferably between 4 phr and 10 phr.

For the purposes of the present description and the claims, theexpression “phr” is intended to indicate the parts by weight of a givencomponent of the elastomeric composition per 100 parts by weight ofelastomeric base.

According to one preferred embodiment, the elastomeric polymercontaining epoxide groups (which is also referred to for simplicityhereinbelow as “epoxidized elastomeric polymer”) is chosen fromhomopolymers and copolymers with elastomeric properties having a glasstransition temperature (T_(g)) of less than 23° C. and preferably lessthan 0° C. Said epoxidized elastomeric polymer generally contains atleast 0.05 mol %, preferably from 1 mol % to 70 mol %, even morepreferably from 5 mol % to 60 mol %, of epoxide groups relative to thetotal number of moles of monomers present in the polymer. Blends ofvarious elastomeric polymers containing epoxide groups, or blends of oneor more epoxidized elastomeric polymers with one or more non-epoxidizedelastomeric polymers, also fall within the present definition.

In the case of copolymers, these may have a random, block, grafted oralso mixed structure. The average molecular weight of the elastomericpolymer containing epoxide groups is preferably between 10 000 and 1 000000, more preferably between 50 000 and 500 000.

Epoxidized diene homopolymers or copolymers in which the base polymerstructure, of synthetic or natural origin, is derived from one or moreconjugated diene monomers, optionally copolymerized with monovinylarenesand/or polar comonomers, are preferred in particular.

Polymers derived from the (co)polymerization of diene monomerscontaining from 4 to 12, preferably from 4 to 8 carbon atoms, chosen,for example, from: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and the like, or mixturesthereof, are particularly preferred. 1,3-butadiene and isoprene areparticularly preferred.

Monovinylarenes which can optionally be used as comonomers generallycontain from 8 to 20, preferably from 8 to 12, carbon atoms and can bechosen, for example, from: styrene; 1-vinylnaphthalene;2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl orarylalkyl derivatives of styrene, such as, for example: 3-methylstyrene,4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene,2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene; andthe like; or mixtures thereof. Styrene is particularly preferred. Thesemonovinylarenes can optionally be substituted with one or morefunctional groups, such as alkoxy groups, for example 4-methoxystyrene,amino groups, for example 4-dimethylaminostyrene, and the like.

Various polar comonomers can be introduced into the base polymerstructure, in particular vinylpyridine, vinylquinoline, acrylic andalkylacrylic acid esters, nitriles, and the like, or mixtures thereof,such as, for example: methyl acrylate, ethyl acrylate, methylmethacrylate, ethyl methacrylate, acrylonitrile, and the like.

Among the base polymer structures which are particularly preferred are:natural rubber, polybutadiene, polyisoprene, styrene/butadienecopolymers, butadiene/isoprene copolymers, styrene/isoprene copolymers,nitrile rubbers, and the like, or blends thereof.

In the case of copolymers, the amount of diene comonomer relative to theother comonomers is such as to ensure that the final polymer haselastomeric properties. In this sense, it is not possible generally toestablish the minimum amount of diene comonomer required to obtain thedesired elastomeric properties. As a guide, an amount of diene comonomerof at least 50% by weight relative to the total weight of the comonomerscan generally be considered sufficient.

The preparation of the base diene polymer may be carried out accordingto known techniques, generally in emulsion, in suspension or insolution. The base polymer thus obtained is then subjected toepoxidation according to known techniques, for example by reaction insolution with an epoxidizing agent. This agent is generally a peroxideor a peracid, for example m-chloroperbenzoic acid, peracetic acid, andthe like, or alternatively hydrogen peroxide in the presence of acarboxylic acid or a derivative thereof, for example acetic acid, aceticanhydride and the like, optionally mixed with an acid catalyst such assulphuric acid. Further details regarding processes for epoxidizingelastomeric polymers are disclosed, for example, in U.S. Pat. No.4,341,672 or by Schulz et al. in “Rubber Chemistry and Technology”, Vol.55, pages 809 et seq.

Polymers containing epoxide groups which may also be used includeelastomeric copolymers of one or more monoolefins with an olefiniccomonomer containing one or more epoxide groups. The monoolefins may bechosen from: ethylene and x-olefins generally containing from 3 to 12carbon atoms, such as, for example: propylene, 1-butene, 1-pentene,1-hexene, 1-octene and the like, or mixtures thereof. The following arepreferred: copolymers between ethylene and an α-olefin, and optionally adiene; homopolymers of isobutene or copolymers thereof with smallamounts of a diene, which are optionally at least partially halogenated.The diene optionally present generally contains from 4 to 20 carbonatoms and is preferably chosen from: 1,3-butadiene, isoprene,1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene,5-methylene-2-norbornene, and the like. Among these, the following areparticularly preferred: ethylene/propylene copolymers (EPR) orethylene/propylene/diene copolymers (EPDM); polyisobutene; butylrubbers; halobutyl rubbers, in particular chlorobutyl or bromobutylrubbers; and the like, or blends thereof. Olefinic comonomers containingepoxide groups may be chosen, for example, from: glycidyl acrylate,glycidyl methacrylate, vinylcyclohexene monoxide, allyl glycidyl etherand methallyl glycidyl ether. The introduction of the epoxide groups bymeans of the abovementioned epoxidized comonomers may be carried out bycopolymerization of the corresponding monomers according to knowntechniques, in particular by radical copolymerization in emulsion. Whena diene comonomer is present, this comonomer may be used to introduceepoxide groups by means of an epoxidation reaction as described above.

According to one particularly preferred embodiment, said epoxidizedelastomeric polymer is epoxidized natural rubber (ENR).

Examples of epoxidized elastomeric polymers which may be used in thepresent invention and which are currently commercially available are theEpoxyprene® products from Guthrie (epoxidized natural rubber—ENR).

The amount of epoxidized elastomeric polymer present in the elastomericcomposition varies as a function of the amount of functional groupspresent and of the elastic properties which it is intended to obtain forthe final manufactured product. Preferably, the amount of saidepoxidized elastomeric polymer is between 30 phr and 100 phr, morepreferably between 50 phr and 100 phr, even more preferably between 70phr and 100 phr.

As stated above, the elastomeric composition may also comprise at leastone diene elastomer not containing epoxide groups, of natural orsynthetic origin, chosen, for example, from: natural rubber;polybutadiene; polyisoprene; styrene/butadiene copolymers;butadiene/isoprene copolymers; styrene/isoprene copolymers; butylrubbers or halobutyl rubbers; nitrile rubbers; ethylene/propylenecopolymers; ethylene/propylene/non-conjugated diene (such as, forexample, norbornene, cyclooctadiene or dicyclopentadiene) terpolymers;and the like, or blends thereof. Natural rubber and polyisoprene arepreferred. Preferably, said diene elastomer not containing epoxidegroups is present in the elastomeric composition in an amount of between0 phr and 70 phr, more preferably between 10 phr and 50 phr.

As mentioned above, the elastomeric composition may also comprise atleast one reinforcing filler such as, for example, carbon black, silica,alumina, alumino-silicates, calcium carbonate, kaolin, and the like, ormixtures thereof, and preferably carbon black. Preferably, saidreinforcing filler is present in the elastomeric composition in anamount of between 50 phr and 150 phr, more preferably between 60 phr and100 phr.

As mentioned above, the elastomeric composition may also comprise atleast one thermosetting resin. Preferably, said thermosetting resin isof the type such as resorcinol plus methylene donor, both in thetwo-component form (which then forms the thermosetting resin in situ)and in the precondensed form (condensed before being added to saidelastomeric composition). Typically, the methylene donor ishexamethoxymethylmelamine (HMMM) or hexamethylenetetramine (HMT).Alternatively, thermosetting resins of other types such as, for example,epoxide/polyol, epoxide/diamine and epoxide/dicarboxylic acid resins; orresins obtained from the reaction of an alcohol with a diacid (alkydresins); or phenolic resins obtained from the condensation of anoptionally substituted phenol with an aldehyde such as, for example,formaldehyde, acetaldehyde, furfural, may also be used. In this casealso, the two components may be added in situ or the resin precondensedbeforehand may be added to the elastomeric composition. Preferably, saidthermosetting resin is present in the elastomeric composition in anamount of between 0.5 phr and 15 phr, more preferably between 2 phr and10 phr.

Said elastomeric composition also comprises a vulcanizing system chosenfrom those commonly used for diene elastomers. Said vulcanizing systemgenerally comprises a sulphur-based vulcanizing agent together with oneor more vulcanization activators and/or accelerators.

The vulcanizing agent more advantageously used is sulphur, or moleculescontaining sulphur (sulphur donors), with accelerators and activatorsthat are known to those skilled in the art.

Activators that are particularly effective are zinc compounds, and inparticular ZnO, ZnCO₃, zinc salts of saturated or unsaturated fattyacids containing from 8 to 18 carbon atoms such as, for example, zincstearate, preferably formed in situ in the blend using ZnO and fattyacid. Other activators may be chosen from: BiO, PbO, Pb₃O₄, PbO₂, andmixtures thereof.

Accelerators that are commonly used may be chosen from:dithiocarbamates, guanidine, thiourea, thiazoles, sulphenamides,thiurams, amines, xanthates, and the like, or mixtures thereof.

Said elastomeric composition may also comprise other conventionalcomponents, such as antioxidants, anti-ageing agents, protecting agents,plasticizers, compatibilizers for the reinforcing filler, adhesives,anti-ozone agents, modifying resins, lubricants (for example mineraloils, vegetable oils, synthetic oils and the like, or mixtures thereof).

The abovementioned elastomeric composition may be prepared by mixingtogether the polymeric components with the reinforcing filler optionallypresent and with the other additives, according to techniques known inthe art. The mixing may be carried out, for example, using an openblender of open-mill type, or an internal blender of the type withtangential rotors (Banbury) or with interlocking rotors (Intermix), oralternatively in continuous blenders of the Ko-kneader (Buss) orco-rotating or counter-rotating twin-screw type.

The present invention will now be further illustrated with the aid of anumber of embodiment examples, with reference to the attached FIG. 1,which shows a view in cross section of a portion of a tyre madeaccording to the invention.

“a” indicates an axial direction and “r” indicates a radial direction.For simplicity, FIG. 1 shows only a portion of the tyre, the remainingportion not shown being identical and symmetrically arranged withrespect to the radial direction “r”.

The tyre (100) comprises at least one carcass ply (101) whose oppositelateral edges are associated with respective bead wires (102). Theassociation between the carcass ply (101) and the bead wires (102), inthis case, is achieved by folding back the opposite lateral edges of thecarcass ply (101) around the bead wires (102), so as to form the socalled carcass back-folds (101 a) as shown in FIG. 1.

Alternatively, the conventional bead wires (102) may be replaced with apair of circumferentially inextensible annular inserts formed fromelongate elements arranged in concentric coils (not shown in FIG. 1)(see, for example, European patent applications EP 928 680 and EP 928702). In this case, the carcass ply (101) is not back-folded around saidannular inserts, the coupling being provided by a second carcass ply(not shown in FIG. 1) applied externally onto the first ply.

The carcass ply (101) is generally made of a plurality of reinforcingcords arranged parallel to each other and at least partially coated witha layer of elastomeric compound. These reinforcing cords are usuallymade of textile fibres such as, for example, rayon, nylon, polyethyleneterephthalate, or of steel wires which are stranded together, coatedwith a metal alloy (for example copper/zinc, zinc/manganese,zinc/molybdenum/cobalt alloys and the like.

According to a preferred embodiment, said carcass ply (101) comprises aplurality of reinforcing cords coated with a vulcanized elastomericcomposition comprising at least one elastomeric polymer containingepoxide groups.

The rubberized carcass ply (101) is usually of radial type, that is tosay it incorporates reinforcing cords arranged in a substantiallyperpendicular direction relative to a circumferential direction. Eachbead wire (102) is encased in a bead (103), defined along an innercircumferential edge of the tyre (100), with which the tyre engages on arim (not shown in FIG. 1) forming part of a vehicle wheel. The spacedefined by each carcass back-fold (101 a) contains a bead filler (104),made according to the invention, in which are embedded the bead wires(102). An antiabrasive strip (105) is usually placed in an axiallyexternal position relative to the carcass back-fold (101 a).

Along the circumference of the rubberized carcass ply (101) is applied abelt structure (106). In the particular embodiment in FIG. 1, the beltstructure (106) comprises two belt strips (106 a, 106 b) whichincorporate a plurality of reinforcing cords, typically metal cords,which are parallel to each other in each strip and intersecting withrespect to the adjacent strip, oriented so as to form a predeterminedangle relative to a circumferential direction. On the radially outermostbelt strip (106 b) may optionally be applied at least one zero-degreereinforcing layer (106 c), commonly known as a “0° belt”, whichgenerally incorporates a plurality of reinforcing cords, typicallytextile cords, arranged at an angle of a few degrees relative to acircumferential direction, and coated and welded together by means of anelastomeric material.

A sidewall (108) is also applied externally onto the rubberized carcassply (101), this sidewall extending, in an axially external position,from the bead (103) to the end of the belt structure (106).

A tread band (109), whose lateral edges are connected to the sidewalls(108), is applied circumferentially to the belt structure (106) in aradially external position. Externally, the tread band (109) has arolling surface (109 a) designed to come into contact with the ground.Circumferential grooves which are connected by transverse notches (notshown in FIG. 1) so as to define a plurality of blocks of various shapesand sizes distributed over the rolling surface (109 a) are generallymade in this surface (109 a), which is represented for simplicity inFIG. 1 as being smooth.

A strip made of elastomeric material (110), commonly known as a“mini-sidewall”, may optionally be present in the connecting zonebetween the sidewalls (108) and the tread band (109), this mini-sidewallgenerally being obtained by co-extrusion with the tread band andallowing an improvement in the mechanical interaction between the treadband (109) and the sidewalls (108). Alternatively, the end portion ofthe sidewall (108) directly covers the lateral edge of the tread band(109). A underlayer which forms, with the tread band (109), a structurecommonly known as a “cap and base” (not shown in FIG. 1) may optionallybe placed between the belt structure (106) and the tread band (109).

A layer of elastomeric material (111) which serves as an “attachmentsheet”, i.e. a sheet capable of providing the connection between thetread band (109) and the belt structure (106), may be placed between thetread band (109) and the belt structure (106).

In the case of tubeless tyres, a rubber layer (112) generally known as a“liner”, which provides the necessary impermeability to the inflationair of the tyre, may also be provided in a radially internal positionrelative to the rubberized carcass ply (101).

The process for producing the tyre according to the present inventionmay be carried out according to techniques and using apparatus that areknown in the art, as described, for example, in patents EP 199 064, U.S.Pat. No. 4,872,822 and U.S. Pat. No. 4,768,937, said process includingat least one stage of manufacturing the green tyre and at least onestage of vulcanizing this tyre.

More particularly, the process for producing the tyre comprises thestages of preparing beforehand and separately from each other a seriesof semi-finished articles corresponding to the various parts of the tyre(carcass plies, belt structure, bead wires, fillers, sidewalls and treadband) which are then combined together using a suitable manufacturingmachine. Next, the subsequent vulcanization stage welds theabovementioned semi-finished articles together to give a monolithicblock, i.e. the finished tyre.

Naturally, the stage of preparing the abovementioned semi-finishedarticles is preceded by a stage of preparing and moulding the variousmixtures which are the constituents of said semi-finished articles,according to conventional techniques.

The green tyre thus obtained then goes through the subsequent stages ofmoulding and vulcanization. To this end, a vulcanization mould is usedwhich is designed to receive the tyre being processed inside a mouldingcavity having walls which are countermoulded and which define the outersurface of the tyre when the vulcanization is complete.

Alternative processes for producing a tyre or parts of a tyre withoutusing semi-finished articles are disclosed, for example, in theabovementioned patent applications EP 928 680 and EP 928 702.

The green tyre may be moulded by introducing a pressurized fluid intothe space defined by the inner surface of the tyre, so as to press theouter surface of the green tyre against the walls of the mouldingcavity. In one of the moulding methods widely practised, a vulcanizationchamber made of elastomeric material, filled with steam and/or anotherfluid under pressure, is inflated inside the tyre closed inside themoulding cavity. In this way, the green tyre is pushed against the innerwalls of the moulding cavity, thus obtaining the desired moulding.Alternatively, the moulding can be carried out without an inflatablevulcanization chamber, by providing inside the tyre a toroidal metalsupport shaped according to the configuration of the inner surface ofthe tyre to be obtained (see, for example, patent EP 242 840). Thedifference in coefficient of thermal expansion between the toroidalmetal support and the crude elastomeric material is exploited to achievean adequate moulding pressure.

At this point, the stage of vulcanizing the crude elastomeric materialpresent in the tyre is carried out. To this end, the outer wall of thevulcanization mould is placed in contact with heating fluid (generallysteam) such that the outer wall reaches a maximum temperature generallyof between 100° C. and 230° C. Simultaneously, the inner surface of thetyre is heated to the vulcanization temperature using the samepressurized fluid used to press the tyre against the walls of themoulding cavity, heated to a maximum temperature of between 100° C. and250° C. The time required to obtain a satisfactory degree ofvulcanization throughout the mass of the elastomeric material may varyin general between 3 minutes and 90 minutes and depends mainly on thedimensions of the tyre. When the vulcanization is complete, the tyre isremoved from the vulcanization mould.

Although the present invention has been illustrated in relation to atyre, the vulcanized elastomeric manufactured products described abovemay be conveyor belts, drive belts, flexible tubes, etc.

The present invention will be further illustrated below by means of anumber of preparation examples, which are given for pure indicativepurposes and without any limitation of this invention.

EXAMPLES 1-3

Preparation of the Mixtures

The elastomeric compositions given in Table 1 (the amounts of thevarious components are expressed in phr) were prepared by mixingtogether the elastomeric polymers (NR and ENR 25), the carbon black(N375), the fibres (Kevlar® Engineered Elastomer) and the thermosettingresin in a tangential internal mixer for about 5 minutes, reaching afinal temperature of about 150° C. Next, said compositions weredischarged from the internal mixer, introduced into a laboratoryopen-mill blender and the other components (given in Table 1) wereadded: the whole was mixed for about 3 minutes at 100° C. TABLE 1INGREDIENTS EXAMPLE 1* EXAMPLE 2* EXAMPLE 3 NR 100.0  80.00  — ENR 25 —— 80.00  KEVLAR ® — 26.00  26.00  N375 75.0 75.00  75.00  STEARIC ACID 2.0 1.50 1.50 ZnO 10.0 6.00 6.00 PHENOLIC RESIN 18.0 — — COBALT  5.7 —— NAPHTHENATE AROMATIC OIL  1.5 — — HMT  1.8 1.54 1.54 RESORCINOL — 1.211.21 ADHESIVE  2.0 2.00 2.00 ANTIOXIDANT  3.0 3.00 3.00 TBBS  1.0 1.001.00 SULPHUR  7.0 3.30 3.30 RETARDANT  0.4 0.30 0.30*: comparative.NR: natural rubber;ENR 25: epoxidized natural rubber containing 25 mol % of epoxide groups(Epoxyprene ® 25 from Guthrie);Kevlar ® Engineered Elastomer: blend of 23% by weight of Kevlar ® and77% by weight of natural rubber (Du Pont);N375: carbon black;Phenolic resin: octylphenolic resin (Durez ® 29095 from (Occidental);HMT: hexamethylenetetramine;Adhesive: t-butylphenol formaldehyde (Durez ® 32333 from (Occidental);Antioxidant: 6-p-phenylenediamine (Santoflex ® 13 from Monsanto);TBBS: N-t-butyl-2-benzothiazyl sulphenamide (Vulkacit ® NZ from Bayer);Retardant: cyclohexylthiophthalimide (Vulkalent ® G from Bayer).

The compositions thus prepared were subjected to MDR rheometric analysisusing an MDR rheometer from Monsanto, the tests being carried out at200° C. for 30 minutes, with an oscillation frequency of 1.66 Hz (100oscillations per minute) and an oscillation amplitude of ±0.5°. Therheometric properties were measured according to ASTM standard D5289-95.

The percentage of reversion was determined according to the followingformula:${{reversion}{\quad\quad}\%} = {\frac{M_{H} - M_{final}}{M_{H} - M_{L}} \times 100}$in which:

-   -   M_(H)=maximum torque value;    -   M_(final)=final torque value;    -   M_(L)=minimum torque value

The Shore D hardness at 23° C. was measured on samples of theabovementioned compositions vulcanized at 150° C. for 30 minutes,according to standard ISO 48. The results are given in Table 2.

Table 2 also gives the elastic properties, measured using an Instrondynamic machine in traction-compression, according to the followingmethods. To this end, samples of the abovementioned compositionsvulcanized at 150° C. for 30 minutes, having a cylindrical shape(length=25 mm; diameter=14 mm), preloaded in compression up to alongitudinal deformation of 10% relative to the initial length, andmaintained at a preset temperature (70° C. or 100° C.) throughout thetest, were subjected to a dynamic sinusoidal deformation with anamplitude of ±3.33% relative to the length under pre-loading, with afrequency of 100 Hz. The elastic properties are expressed in terms ofdynamic elastic modulus values (E′).

Table 2 also gives the load values measured at 50% elongation in thedirection of calendering (M1) and in the direction perpendicular thereto(M2). These load values were obtained in accordance with ASTM standardD412, by subjecting samples of Dunbell type, which were obtained byvulcanizing samples of the abovementioned compositions at 150° C. for 30minutes, to traction. TABLE 2 EXAMPLE 1* 2* 3 RHEOMETRIC PROPERTIESM_(L) (dN · m) 3.06 5.47 4.59 M_(H) (dN · m) 67.01 47.19 55.66 M_(final)(dN · m) 28.96 27.9 39.7 TS2 (min) 0.23 0.32 0.32 T90 (min) 0.70 0.670.66 REVERSION (%) 59.50 46.42 31.10 MECHANICAL PROPERTIES Load M1 at50% elongation 8.06 11.22 14.74 in the direction of calendering (MPa)Load M2 at 50% elongation 7.50 7.88 10.51 in the direction perpendicularto calendering (MPa) M1/M2 1.07 1.42 1.40 ELASTIC PROPERTIES E′ (70° C.)(MPa) 59.59 25.36 35.58 E′ (100° C.) (MPa) 47.61 23.02 30.70 Shore Dhardness at 23° C. 48.00 51.00 55.00*: comparative.

From the experimental results given in Table 2, it may be seen that theuse of epoxidized natural rubber makes it possible to obtain elastomericcompositions which have improved mechanical properties, in particular abetter load at elongation, and better elastic properties, in particulara better dynamic elastic modulus at high temperature, and also a lowerpercentage of reversion with respect to the comparative elastomericcompositions.

EXAMPLE 4

Evaluation of the Performance Qualities on the Road

Tyres according to the invention of the type Pirelli® P3000® 175/65 R14were prepared using, as bead filler, the compositions of Example 1(comparative) and of Example 3.

The following tests were carried out: handling on wet surface,straight-line driving, behaviour driving at normal speed (softhandling), behaviour at the limit of adherence (hard handling) andcomfort. The term “hard handling” indicates the execution by the testdriver of all the manoeuvres that an average driver may be forced tocarry out in the case of unforeseen and hazardous situations: sharpsteering at high speed, sudden changes of direction and of driving toavoid obstacles, sharp braking and the like.

The abovementioned tests were carried out at the Vizzola Ticino testtrack as regards the wet surface tests (road holding on a wet surfaceand track lap time on a wet surface), and at the Imola test track asregards the dry surface tests, the tyres being mounted on a 1400 cc FiatBrava car.

The reference tyres and test tyres were tested by an independent pair oftest drivers who subsequently awarded the tyres a grade from 0 to 10based on their subjective opinion for each test carried out. Once thegrading was complete, an index of 100 was given to the reference tyres.A percentage increase in the index was then assigned to the test tyresin proportion to the improvement in performance qualities during thetest. In other words, the higher the index, the better the performancequalities offered by the tyre under examination.

The test results, expressed as the average of the grades awarded by thetwo test drivers, are given in Table 3. TABLE 3 TESTS EXAMPLE 1* EXAMPLE3 Wet surface handling 100 113 Lap time on a wet 100 101 surfaceStraight-line driving 100 117 Soft handling 100 119 Hard handling 100114 Comfort 100 103*: comparative.

The data given above demonstrate that the tyre with the bead filleraccording to the present invention is capable of offering betterperformance qualities than the tyre with the comparative bead filler asregards wet surface handling, straight-line driving and the handling,while keeping the performance qualities substantially identical asregards the track lap time on a wet surface and the comfort.

1. Tyre for vehicle wheels comprising: a carcass structure having atleast one carcass ply shaped in a substantially toroidal configuration,the opposite lateral edges of which are associated with respective leftand right bead wires, each bead wire being enclosed in a respectivebead, said bead comprising a bead filler, wherein said bead filler isobtained by vulcanization of an elastomeric composition comprisingdiscontinuous fibres and at least one elastomeric Polymer containingepoxide groups; a belt structure comprising at least one belt stripapplied circumferentially over said carcass structure; a tread bandcircumferentially superimposed on said belt structure; and a pair ofsidewalls applied laterally on opposite sides relative to said carcassstructure.
 2. Tyre according to claim 1, in which the discontinuousfibres are aramid fibres.
 3. Tyre according to claim 2, in which thearamid fibres are short fibrillated poly(para-phenylene-terephthalamide) fibres.
 4. Tyre according to claim 2,in which the aramid fibres are predispersed in a polymer matrix chosenfrom: natural rubber, butadiene/styrene copolymers, or ethylene/vinylacetate copolymers.
 5. Tyre according to claim 4, in which the polymermatrix is natural rubber.
 6. Tyre according to claim 1, in which thediscontinuous fibres are derived from polyamides other than aramids,polyesters, polyolefins, polyvinyl alcohols, or glass fibres.
 7. Tyreaccording to claim 1, in which the discontinuous fibres are present inan amount of between 2 phr and 12 phr.
 8. Tyre according to claim 7, inwhich the discontinuous fibres are present in an amount of between 4 phrand 10 phr.
 9. Tyre according to claim 1, in which the elastomericpolymer containing epoxide groups is a homopolymer or copolymer withelastomeric properties having a glass transition temperature (Tg) ofless than 23° C.
 10. Tyre according to claim 1, in which the elastomericpolymer containing epoxide groups contains at least 0.05 mol % ofepoxide groups relative to the total number of moles of monomers presentin the polymer.
 11. Tyre according to claim 10, in which the elastomericpolymer containing epoxide groups contains from 1 mol % to 70 mol % ofepoxide groups relative to the total number of moles of monomers presentin the polymer.
 12. Tyre according to claim 1, in which the elastomericpolymer containing epoxide groups has an average molecular weight ofbetween 10,000 and 1,000,000.
 13. Tyre according to claim 12, in whichthe elastomeric polymer containing epoxide groups has an averagemolecular weight of between 50,000 and 500,000.
 14. Tyre according toclaim 1, in which the elastomeric polymer containing epoxide groups isan epoxidized diene homopolymer or copolymer having a base polymerstructure, in which the base polymer structure is derived from one ormore conjugated diene monomers, optionally copolymerized withmonovinylarenes and/or polar comonomers.
 15. Tyre according to claim 14,in which the base polymer structure is chosen from: natural rubber,polybutadiene, polyisoprene, styrene/butadiene copolymers,butadiene/isoprene copolymers, styrene/isoprene copolymers, nitrilerubbers, or blends thereof.
 16. Tyre according to claim 13, in which theelastomeric polymer containing epoxide groups is chosen from elastomericcopolymers of one or more monoolefins with an olefinic comonomercontaining one or more epoxide groups.
 17. Tyre according to claim 1, inwhich the elastomeric polymer containing epoxide groups is epoxidizednatural rubber.
 18. Tyre according to claim 1, in which the elastomericpolymer containing epoxide groups is present in an amount of between 30phr and 100 phr.
 19. Tyre according to claim 18, in which theelastomeric polymer containing epoxide groups is present in an amount ofbetween 50 phr and 100 phr.
 20. Tyre according to claim 19, in which theelastomeric polymer containing epoxide groups is present in an amount ofbetween 70 phr and 100 phr.
 21. Tyre according to claim 1, in which theelastomeric composition further comprises at least one diene elastomernot containing epoxide groups.
 22. Tyre according to claim 21, in whichthe diene elastomer not containing epoxide groups is chosen from:natural rubber; polybutadiene; polyisoprene; styrene/butadienecopolymers; butadiene/isoprene copolymers; styrene/isoprene copolymers;butyl rubbers or halobutyl rubbers; ethylene/propylene copolymers;ethylene/propylene/non-conjugated diene terpolymers; or blends thereof.23. Tyre according to claim 22, in which the diene elastomer notcontaining epoxide groups is natural rubber or polyisoprene.
 24. Tyreaccording to claim 21, in which the diene elastomer not containingepoxide groups is present in an amount of between 0 phr and 70 phr. 25.Tyre according to claim 24, in which the diene elastomer not containingepoxide groups is present in an amount of between 10 phr and 50 phr. 26.Tyre according to claim 1, in which the elastomeric composition furthercomprises at least one reinforcing filler chosen from carbon black,silica, alumina, aluminosilicates, calcium carbonate, kaolin, ormixtures thereof.
 27. Tyre according to claim 26, in which thereinforcing filler is carbon black.
 28. Tyre according to claim 26, inwhich the reinforcing filler is present in an amount of between 50 phrand 150 phr.
 29. Tyre according to claim 28, in which the reinforcingfiller is present in an amount of between 60 phr and 100 phr.
 30. Tyreaccording to claim 1, in which the elastomeric composition furthercomprises at least one thermosetting resin.
 31. Tyre according to claim30, in which the thermosetting resin is of the two-component type. 32.Tyre according to claim 30, in which the thermosetting resin is of theprecondensed type.
 33. Tyre according to claim 30, in which thethermosetting resin is present in an amount of between 0.5 phr and 15phr.
 34. Tyre according to claim 33, in which the thermosetting resin ispresent in an amount of between 2 phr and 10 phr.
 35. Tyre according toclaim 1, in which the carcass ply further comprises a plurality ofreinforcing cords coated with a vulcanized elastomeric compositioncomprising at least one elastomeric polymer containing epoxide groups.36. Tyre according to claim 35, in which the elastomeric polymercontaining epoxide groups is a homopolymer or copolymer with elastomericproperties having a glass transition temperature (Tg) of less than 23°C.
 37. Elastomeric composition comprising: discontinuous fibres, and atleast one polymer containing epoxide groups.
 38. Elastomeric compositionaccording to claim 37, in which the elastomeric polymer containingepoxide groups is a homopolymer or copolymer with elastomeric propertieshaving a glass transition temperature (Tg) of less than 23° C. 39.Elastomeric composition according to claim 37, further comprising atleast one diene elastomer not containing epoxide groups.
 40. Elastomericcomposition according to claim 39, in which the diene elastomer notcontaining epoxide groups is chosen from: natural rubber; polybutadiene;polyisoprene; styrene/butadiene copolymers; butadiene/isoprenecopolymers; styrene/isoprene copolymers; butyl rubbers or halobutylrubbers; ethylene/propylene copolymers;ethylene/propylene/non-conjugated diene terpolymers; or blends thereof.41. Elastomeric composition according to claim 39, further comprising atleast one reinforcing filler.
 42. Elastomeric composition according toclaim 41, in which the reinforcing filler is chosen from carbon black,silica, alumina, aluminosilicates, calcium carbonate, kaolin, ormixtures thereof.
 43. Elastomeric composition according to claim 39,further comprising at least one thermosetting resin.
 44. Elastomericcomposition according to claim 43, in which the thermosetting resin isof the two-component type.
 45. A vulcanized elastomeric manufacturedproduct obtained by a process comprising vulcanizing an elastomericcomposition of claim
 39. 46. Elastomeric composition according to claim39, in which the diene elastomer not containing epoxide groups ispresent in an amount of between 0 phr and 70 phr.
 47. Elastomericcomposition according to claim 46, in which the diene elastomer notcontaining epoxide groups is present in an amount of between 10 phr and50 phr.
 48. Elastomeric composition according to claim 41, in which thereinforcing filler is present in an amount of between 50 phr and 150phr.
 49. Elastomeric composition according to claim 48, in which thereinforcing filler is present in an amount of between 60 phr and 100phr.
 50. Elastomeric composition according to claim 43, in which thethermosetting resin is of the precondensed type.
 51. Elastomericcomposition according to claim 43, in which the thermosetting resin ispresent in an amount of between 0.5 phr and 15 phr.
 52. Elastomericcomposition according to claim 51, in which the thermosetting resin ispresent in an amount of between 2 phr and 10 phr.
 53. Tyre according toclaim 35, in which the elastomeric polymer containing epoxide groupscontains at least 0.05 mol % of epoxide groups relative to the totalnumber of moles of monomers present in the polymer.
 54. Tyre accordingto claim 53, in which the elastomeric polymer containing epoxide groupscontains from 1 mol % to 70 mol % of epoxide groups relative to thetotal number of moles of monomers present in the polymer.
 55. Tyreaccording to claim 35, in which the elastomeric polymer containingepoxide groups has an average molecular weight of between 10,000 and1,000,000.
 56. Tyre according to claim 55, in which the elastomericpolymer containing epoxide groups has an average molecular weight ofbetween 50,000 and 500,000.
 57. Tyre according to claim 35, in which theelastomeric polymer containing epoxide groups is an epoxidized dienehomopolymer or copolymer having a base polymer structure, in which thebase polymer structure is derived from one or more conjugated dienemonomers, optionally copolymerized with monovinylarenes and/or polarcomonomers.
 58. Tyre according to claim 57, in which the base polymerstructure is chosen from: natural rubber, polybutadiene, polyisoprene,styrene/butadiene copolymers, butadiene/isoprene copolymers,styrene/isoprene copolymers, nitrile rubbers, or blends thereof. 59.Tyre according to claim 35, in which the elastomeric polymer containingepoxide groups is chosen from elastomeric copolymers of one or moremonoolefins with an olefinic comonomer containing one or more epoxidegroups.
 60. Tyre according to claim 35, in which the elastomeric polymercontaining epoxide groups is epoxidized natural rubber.
 61. Tyreaccording to claim 35, in which the elastomeric polymer containingepoxide groups is present in an amount of between 30 phr and 100 phr.62. Tyre according to claim 61, in which the elastomeric polymercontaining epoxide groups is present in an amount of between 50 phr and100 phr.
 63. Tyre according to claim 62, in which the elastomericpolymer containing epoxide groups is present in an amount of between 70phr and 100 phr.
 64. Tyre according to claim 37, in which theelastomeric polymer containing epoxide groups contains at least 0.05 mol% of epoxide groups relative to the total number of moles of monomerspresent in the polymer.
 65. Tyre according to claim 53, in which theelastomeric polymer containing epoxide groups contains from 1 mol % to70 mol % of epoxide groups relative to the total number of moles ofmonomers present in the polymer.
 66. Tyre according to claim 37, inwhich the elastomeric polymer containing epoxide groups has an averagemolecular weight of between 10,000 and 1,000,000.
 67. Tyre according toclaim 66, in which the elastomeric polymer containing epoxide groups hasan average molecular weight of between 50,000 and 500,000.
 68. Tyreaccording to claim 37, in which the elastomeric polymer containingepoxide groups is an epoxidized diene homopolymer or copolymer having abase polymer structure, in which the base polymer structure is derivedfrom one or more conjugated diene monomers, optionally copolymerizedwith monovinylarenes and/or polar comonomers.
 69. Tyre according toclaim 68, in which the base polymer structure is chosen from: naturalrubber, polybutadiene, polyisoprene, styrene/butadiene copolymers,butadiene/isoprene copolymers, styrene/isoprene copolymers, nitrilerubbers, or blends thereof.
 70. Tyre according to claim 37, in which theelastomeric polymer containing epoxide groups is chosen from elastomericcopolymers of one or more monoolefins with an olefinic comonomercontaining one or more epoxide groups.
 71. Tyre according to claim 37,in which the elastomeric polymer containing epoxide groups is epoxidizednatural rubber.
 72. Tyre according to claim 37, in which the elastomericpolymer containing epoxide groups is present in an amount of between 30phr and 100 phr.
 73. Tyre according to claim 72, in which theelastomeric polymer containing epoxide groups is present in an amount ofbetween 50 phr and 100 phr.
 74. Tyre according to claim 73, in which theelastomeric polymer containing epoxide groups is present in an amount ofbetween 70 phr and 100 phr.